I tried high settings but there is some lag when there are heavy explosions and smoke and stuff. 5700 can handle medium settings easily atleast up to 1680x1050 which is my asus monitor native resolution. If someone has one of those fullhd monitors that support 1900xsomething post if 5770 can handle this higher resolution.

The 5770, while a strong card, is not "specifically" meant for gaming alone. The 5800 and 5900 series cards are pure gamers through and through. Still, you should get pretty decent FPS with that thing. I'm not an intel guy, but you might be bottlenecked somewhere? What board are you running and what are your RAM timings set at?

I have a Q9550 @4ghz with 4GB DDR2800 running @925mhz with a 5770 and I run everything on high 2xAA 16xAF at 1920x1080 and the only time I notice a slowdown is when a building is getting demolished by a mortar strike. The Physics really take a toll on this graphics card...